Misapplied analogy.
Its more like a baker refusing to let gay people eat cup cakes they make in the store.
The baker refusing to make a custom cake for a gay wedding ceremony would be more like Queen refusing to play live at the RNC convention.
There is more than one moral principle involved. There is a distinction to be made between allowing somebody to avail themselves of a product you produce for general consumption, and providing custom service that is essentially participation and implicit endorsement.
Trump playing Queen's song does not imply Queen endorses him or is participating in the convention. Queen coming to play for his convention does.
A Christian baker selling cup cakes to people in the store who happen to be a gay "married" couple is not an implied endorsement or participation in their "marriage". The baker baking and decorating the wedding cake of a gay "marriage" does.
I can’t say we can agree on this.
It’s the same thing.
1) Baker avails himself of becoming a public place of accommodation then he opens his shop and bakes a cake.
2) Artist avails themselves to having their songs become part of the public domain once they sell their songs to the public.
3) Once the works either it be a cake or a song are available for public consumption, the baker and artist can not discriminate as to who can purchase their goods.
4) Refusing to allow a song to be played and refusing to bake a cake are in essence the same thing. Both goods are open for purchase by the public. Once that happens, you can not discriminate as to who buys your product.
There’s no discernible difference between the two.